Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1.5–2.5
New glide avalanches continue to be observed daily in Girdwood, Turnagain Pass, Summit Lake, and Seward. Glide avalanches aside, the last known avalanche activity in the Summit Lake zone was almost two weeks ago, when two separate groups triggered large avalanches remotely on Tenderfoot Ridge.
We're in a bit of a holding pattern with these persistent weak layers of buried surface hoar. There are actually three layers of buried surface hoar in the upper 3' of the snowpack, and any of those may still produce large avalanches. It has been over a week since the last known avalanche failed any of these weak layers, but with so little traffic in the backcountry since last weekend it is really hard to say if that's because they're gaining strength, or if it's just because people haven't been getting into the terrain where the layer is problematic. Most likely it is some kind of combination of both.
Based on what we've been seeing in snowpits, we know these layers are still present, and it is likely there are still plenty of steep, upper elevation slopes where a person can trigger a large avalanche. These layers are notorious for giving misleading results in a snowpit even when conditions are dangerous, and they may not give any warning signs before someone triggers a big avalanche. The most suspect habitat for this weak layer lies in steep terrain above around 2500'. Keep this dangerous setup on your mind if you are headed into the alpine to get to the good surface conditions. For now, we're still avoiding traveling in steep, complex terrain while we suss out just how reactive the snowpack still is.
Wind Slabs: We are expecting to see northeasterly winds pick up this afternoon into tonight. These will start to blow snow into reactive slabs up to a foot deep in upper-elevation start zones, especially just below ridgelines, in steep gullies, and below convex rollovers. While not nearly as big as the other avalanches we are concerned with, this is another thing that will be important to pay attention to as the winds pick up.
(12/1/2025)
Buried surface hoar from a hand pit on Tenderfoot Ridge, at about 2200' elevation. This layer was a little over a foot deep.
Photo: Mik Dalpes